Conventionally, an inorganic photoreceptor comprising an inorganic photosensitive layer composed of an inorganic photoconductive compound, such as selenium, zinc oxide or cadmium sulfide, has been widely used as an electrophotographic photoreceptor.
Such an inorganic photoreceptor, however, is not always satisfactory in respect of the sensitivity, thermal stability, moisture resistance and durability. For example, an inorganic photoreceptor having a selenium photosensitive layer, when placed under a high temperature condition, tends to be crystallized, thus deteriorating the characteristics as of an electrophotographic photoreceptor, so that the manufacturing process thereof needs a strict temperature control and to be prevented from being crystallized due to heat or finger prints in handling. Also, an inorganic photoreceptor having an inorganic photosensitive layer comprised of cadmium sulfide or zinc oxide is inferior in the moisture resistance and durability.
Due to such circumstances, the research and development of organic photoreceptors having an organic photosensitive layer containing an organic photoconductive compound have been extensively carried on in recent years.
For example, Japanese Patent Examined Publication No. 10496/1975 discloses an organic photoreceptor having an organic photosensitive layer containing poly-N-vinylcarbazole and 2,4,7-trinitro-9-fluorenone. The organic photoreceptor, however, is still inadequate in the photosensitivity and durability.
On the other hand, an organic photoreceptor having a function separation-type organic photosensitive layer, containing two different materials, one for a carrier, positive hole or electron, generation function and the other for a carrier, positive hole or electron, transport function, have been developed lately.
Such an organic photoreceptor has the advantage that the range of choice of a material to constitue the photosensitive layer is so much wide that any organic photoreceptor having a variety of characteristics can relatively easily be prepared.
As the carrier generation material for carrier generation function, various azo compounds are in practical use, while as the carrier transport material for carrier transport function, there are those materials proposed in Japanese Patent Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 94829/1976, 72231/1977, 27033/1978, 52063/1980, 65440/1983 and 198425/1983.
An organic photoreceptor prepared with the above carrier transport material, however, has the disadvantage that its carrier transportability is inadequate to result in the lowering of the sensitivity or the rise of the residual potential particularly when applied to a high-speed copying process under a low-temperature environmental condition.
Under the circumstances, a technique to use a polysilane of a specific structure as a carrier or positive-hole transport material has recently been proposed; see Japanese Patent O.P.I. Publication No 170747/1986. The polysilane, since it has a self-layer-formability unlike the aforementioned carrier transport material, enables to easily form a film-state photosensitive layer without combination with a binder. And in the silane, the mobility of positive hole is on the order of about 10.sup.-4 cm.sup.2 /V.sec, one figure larger than that of the foregoing carrier transport material, and thus the use of this material solves the disadvantage of the organic photoreceptor constituted with the above-mentioned carrier transport material.
However, a photosensitive layer prepared with the polysilane has problems: One problem is that the layer's strength is generally low, so that, when repeatedly used in an electrophotographic process, the layer surface is damaged or peeled by a scratching force caused by a toner in the development process or by a cleaning member in the cleaning process, and as a result, on the obtained copy image defects such as white or dark streaks appear in an early stage, thus deteriorating the resulting image. Another is that the polysilane has a relatively small dark resistance, so that an organic photoreceptor prepared with the material has an insufficient chargeability.
In order to increase the layer strength of a photosensitive layer, the inventers have attempted to combine the polysilane with other polymer to form a photosensitive layer, but have now found that, in a way of merely mixing both, because of the bad compatibility of the polysilane with other polymers, a phase separation occurs between them, so that no sufficient effect is exhibited.